In the manufacture and marketing of hosiery products, such as socks and anklets, it is commercially important to know which size, or range of sizes, a sock will fit comfortably. Put another way, it is important to know if a sock will fit comfortably the size, or range of sizes, that it is specified to fit.
The National Association of Hosiery Manufacturers has developed a set of standard size forms to facilitate the testing for the fit of below-the-knee hosiery, i.e. socks and anklets. Each form represents a particular size foot and leg and is designed so that its critical surface dimensions approximate those of a human foot and leg of the same size. When a sock fits one of these standard size forms, without being unduly loose or tight, the sock can be said to fit a human foot of the same size. These standard size forms have been widely accepted by the hosiery industry as the standard for determining and measuring size.
It is relatively easy to determine if a sock is too loose because of the presence of wrinkles or areas where the sock does not touch the form. On the other hand, even among skilled and experienced technicians, there often is wide disagreement over whether or not a sock is too tight on a particular form.
Others have recognized the need for determining the tension in the fabric of hosiery articles supported on hosiery forms. For example, a stocking testing device is disclosed in U.S. Pat. No. 2,675,703 which includes a "standard" leg form with pressure strips incorporated in various locations along the form and movable outwardly against the hosiery article positioned thereon to determine the tension applied to the form by the hosiery fabric. However, this type of testing device is very expensive to construct and maintain. U.S. Pat. Nos. 3,975,956 and 4,137,763 disclose hosiery testing devices particularly adapted for testing the compressive force in support hosiery. These testing devices include a form onto which the hosiery article is drawn and the tension in the hosiery article is then tested at various locations along the length of the hosiery form. The testing devices of these patents are also expensive to construct and maintain and are not readily adaptable to use in testing the size of below-the-knee hosiery articles.
Another method in use employs a foot form with the foot portion constructed of two pieces in such a way that the form can be expanded in the lengthwise direction. After the sock is placed on this form and the heel is clamped in place, a measured force is applied to the toe to extend the sock, and this extension is measured. To obtain sufficient accuracy, a relatively large and expensive tensile testing machine, such as is manufactured by Instron, is required. Another drawback of this method is that it is sensitive primarily to fabric tension in the lengthwise or walewise direction while largely ignoring the widthwise or coursewise component of tension.